1. Field of the Invention
The present invention relates to improvements in UV-stable reinforced molding compositions containing impact-modifying elastomeric polymers and fibrous filler such as glass fibers, in order to increase the flow properties thereof while still having good ductility and stiffness. The present compositions are based upon cyclo aliphatic polyester polymer blends with polyether-polyester copolymers as binder materials for the reinforced molding compositions. The blend may optionally contain aromatic polycarbonate polymers.
Thermoplastic polymers have many desirable properties that make them useful in injection molding applications. Some of these desirable properties include strength, toughness, heat resistance, and resistance to chemicals. It is known to add impact modifiers to polyester resins to improve the ductility or the notched Izod impact strength thereof. However the effect of such impact modifiers on reinforcing polyester resin compositions, such as those containing 30% by weight of reinforcing glass fibers, is a relatively modest improvement in ductility and, unfortunately, an increase in the melt viscosity or reduction in the melt flow, modulus and heat distortion properties of the composition.
One problem with polyesters in injection molding applications is that it is sometimes difficult to fill large molds requiring long flow lengths or very thin parts because of the high melt viscosity of the polymer. A solution to this problem is to raise the temperature of the polymer melt, thus lowering its viscosity. This solution is often not satisfactory for polyester polymers since polyesters tend to degrade, or lose molecular weight, at elevated processing temperatures.
Also, there are well known additives which reduce the melt viscosity of polyesters. However, these additives usually make the resulting molded material less rigid, less heat resistant, and/or function only by breaking down the molecular weight of the polyester resulting in reduced impact.
2. Description of Prior Art
Reference is made to commonly-assigned U.S. Pat. No. 5,486,562, the disclosure of which is hereby incorporated herein, for its disclosure of UV-stable weatherable molding compositions based upon PCCD aliphatic polyester binder materials containing impact-modifying elastomeric polymers and filler such as glass fibers, which compositions have enhanced melt flow properties while retaining good impact strength properties.
However, the biggest disadvantage of such compositions, when used to mold elements such as automotive trim and door handles, is the sacrifice of ductility and stiffness, resulting in brittleness, in order to improve the melt flow properties of the glass filled, reinforced molding composition.
Reference is also made to commonly-assigned U.S. Pat. No. 5,122,551, the disclosure of which is also incorporated herein, for its disclosure of glass-filled copolyether-polyester compositions containing copolyetherester elastomers. Reinforced copolyether-polyester compositions generally have superior tensile strength and flexural strength when combined with glass fibers treated with epoxy cyanurate sizing agents, as disclosed in said Patent, but do not have good weatherability.
Finally, reference is made to U.S. Pat. No. 4,342,678 which discloses glass fiber-reinforced thermoplastic molding compositions based upon mixtures of certain cycloaliphatic polyester polymers and glass fibers.